Distance Measuring Equipment - Ch 5

Question 1

DME

Answer 1

Co-located with beacon (VOR) or approach aid

Secondary Radar System

UHF Band 962 - 1213 MHZ (~1000 MHZ)

Question 2

Principle of Operation

Answer 2

AC sends out jittered pulse pairs
Ground transponder sends out jittered pulse pair +/-67MHZ back (takes 50nanosecs)
AC calculates time and then distance

Question 3

Beacon Saturation

Answer 3

Capacity - 2700pps (~100AC) in normal mode

100 of the strongest signals

Question 4

Beacon Modes

Answer 4

Search: Looking for DME response, 150pps (1st 100s) and then 60pps there after until it finds
Tracking: PRF drops to 25pps
Memory: 10s after loss of signal, DME freezes, after 10s lost, returns to search mode

Question 5

Station Identifier

Answer 5

3 letter call sign every 30 secs - in between VOR (3 times in between)

If same site but not co-located, first 2 letters the same plus Z

Question 6

DME Range and Accuracy

Answer 6

Line of sight

Accuracy: +0.25nm + 1.25% slant range works 95% of the time

Should not exceed 0.2 DME (EASA)

Question 7

Slant Range

Answer 7

Pythagoras

FL->NM = FL/6080

1nm = 6080ft

Question 8

DME Ground Speed

Answer 8

ONly correct GS when tracking directly to/from beacon

Question 9

DME Arc

Answer 9

DME Speed will not change as you will be at the same distance from beacon continuously

Question 10

Radial Fix Greek sign

Answer 10

Theta (VOR)

Question 11

DME Fix Greek Symbol

Answer 11

Rho